Plastic Optical MaterialsSheng-Huei Derek Lu

College of Optical SciencesUniversity of Arizona

Apple iPhone 4 Camera LensApple iPhone 4 Camera Specs:5.0 Mpixels (2592 x 1936)3.85 mm lens focal lengthf/2.8 lens apertureEquivalent 35mm film camera30 mm f/22

Sample image is 2592x1936 pixels (5.0 MP, 4.02:3)

Don't throw away your FourThird, APS-C or full frame SLR Cost is Everything!!

iPhone 4 Camera ModuleGlass cell phone lenses cost $20-$40 in the market.Plastic cost: $3.55 only

Manufacturer: Largan Precision Co., LTD, TaiwanProduct#: 9457FComposition4 Plastic Elements

Very high production volumesInjection Molding: 8-Holes Method8 cavities at the same time

Monthly volume = 207,306 parts

OutlinesPlastic optical material applicationAdvantagesDisadvantagesIssues:Structural StabilityThermal StabilityMoisture AbsorptionInjection MoldingWavefont error budgetReference

What are optical elements made of plastic?Cellphone/ NB/ Car/ Camera LensBar code scanners in CD playersPrismsLED collimatorDiffractive Optical Elements

Main AdvantagesCostProduction volumeWeight reductionAspheric and diffractive surfacesIntegral features can have mounting features or multifunction parts

DisadvantagesLower service temperature than glass - max service 80-130 CLow structural stability - soft, larger deflection while applying force, lower resonant frequency than glassPoor thermal properties high dn/dT, high CTEMoisture AbsorptionLimited material selection

Material Properties of Plastic Optical Element

Plastic Element Structural Stability = 1 g/cm3, E = 3 Gpa (glass: =2.5 g/cm3, E=80 Gpa)Resonant frequency

Plastic with 1/3 resonant frequency than glassDeflection per thickness

Plastic with 10 times deflection than glass

Plastic Element Thermal Stabilitydn/dT = -8.5 ppm/C, CTE = 72 ppm/C, = 0.21 W/mK (glass: dn/dT = 1.86 ppm/C, CTE = 7 ppm/C, = 1 W/mK)Defocus due to one degree change

= 89 ppm/C for plastic, = 3.28 ppm/C for glassLinear thermal distortion of a constant heat flux

Plastic with 50 times thermal deflection than glass

Moisture Absorption Water absorption: change of volume, change of refractive indexThe coefficient of moisture expansion (CME) for PMMA is about 0.5%The change of refractive index for PMMA is about 900 ppm

Cycloolefin Polymer (COP) and Cycloolefin Copolymer (COC) are known as low moisture absorption.

Injection Molding

Surface Imperfections - Melt temperature is too high to cause gas evolution: bubbles - Pressure is too low to cause incomplete filling of mold.Shrinkage - If the part thickness is too thin, part will shrink while cooling. - Applying holding pressure is maintained to compensate for material shrinkage

Tolerance Analysis: wavefont error budget for the plastic optical component

1 mold costs $200,000!

ReferenceSelected plastic optical material characteristics are listed in my tutorial: Tutorial for Plastic Optical Materials

Great reference book: Stefan Bumer etc. Hand Book of Plastic Optics, 2005 WILEY

Formulas: Prof. Burge, Opti 521/421 class note